why 'pass your message'?
Why indeed? In my 200 hours or so of piloting I never heard the phrase, but then I never visited old blighty. This is what I was taught, and experienced, example when leaving the circuit in uncontrolled airspace:
"Hasselt radio, OOG86 leaving the circuit and the frequency, expect back in two hours"
(toggle frequency)
"Brussels information, from the OOG86"
"OOG86 Brussels information"
"Brussels information, goedemiddag mevrouw*, the OOG86 just airborne from Hasselt Kiewit for a local flight Hasselt-Hasselt via Diest, Aarschot, Westerlo. VFR 1500, negative transponder. OOG86.
"G86 be aware of paradropping near Diest. Regional QNH 1015"
"QNH1015, will report leaving your frequency, G86"
and that was extensive, at busy moments one would go even more terse.
* the local language greeting was an old tradition of courtesy, the first to be dropped if the frequency was very busy. You could hear people's background from their accent anyway, most of the time. And it was not relevant, anyway. All R/T in English only, to the surprise of the occasional French visitor.
What value "pass your message" could have added here is quite unclear to me.
NB from my registration/callsign, the Info operator could already tell I was flying an ultralight, so cruising at 100 knots or thereabouts. Many countries have such a system of registration (D-Mxxx is always a motorglider, for example), Germany certainly, Netherlands I think too, other countries I cannot say but there must be some. The UK not, of course, as far as I can tell.